Production of hydrocarbons is usually done through a well drilled from surface to the reservoir. Such a well is cased to prevent collapse of its wall. To facilitate fluid flowing into the well, the part of the well extending into or through the reservoir is either not cased or, when cased, the casing is perforated locally. If the underground formation includes sandstone, production of hydrocarbons may cause the formation minerals such as sand near the well to be loosened and to be entrained by the fluid flow to surface. The entrained material causes wear of the production equipment through which the fluid passes. To enforce the formation so that the amount of loosened material is reduced, the underground formation is treated with a mixture of a resin system.
This treating of an underground formation comprises contacting the underground formation with a resin system comprising monomeric and/or polymeric organic polyepoxides having more than one epoxy group per molecule and a curing agent in a solvent.
British patent specification No. 940,237 discloses a method of treating an underground formation in which the solvent is selected from the group including aliphatic alcohols, such as methanol, ethanol, butanol or isopropanol. The solvent can further comprise a hydrocarbon component for controlling the reaction rate.
In carrying out the method of treating the underground formation, the resin system is supplied through an injection tubular arranged in a well to the formation zone to be treated. The lower end of the injection tubular is suitably fixed in the lower part of the well with a packer arranged above the zone to be treated. The packer furthermore prevents upward flow of the resin system through the annulus between the wall of the well and the tubular. An example of an injection tubular is a coiled tubing. In an alternative embodiment, two packers can be used, wherein one packer is arranged above the zone to be treated and the other below that zone.
The packer used in the method of treating a formation includes an inflatable annular element which is of an elastomer such as a rubber.
It was found that diffusion of the solvents into the elastomer caused degradation of the elastomer and consequently malfunctioning of the packer.
U.S. Pat. No. 3,857,444 discloses a method of treating a formation in which gravel coated with an uncured epoxy resin system is introduced into the formation. The solvent used in this system is monoethylene glycol n-butyl ether (to be referred to as butyl oxitol) or a mixture of amyl acetate and butyl oxitol. A disadvantage of such a system is that under underground conditions an epoxy system with a glycol ether solvent will not cure in a reasonable time. In addition, acetates are incompatible with rubber.
It is an object of the present invention to provide a method of treating an underground formation wherein the solvents used do not have a detrimental effect on the elastomer of the packer during the time the method of treating the formation is carried out.
It is a further object of the present invention to provide a method wherein the resin system does not easily separate; in other words, solvents should e so selected that both the resin as well as the curing agent are completely soluble in the solvent. It is a further object to provide such a method in which the resin system cures in a reasonable amount of time.